 Dancing Chaos  Ivars Peterson (MathTrek)
Music, dance, and chaos... The image on the computer screen resembles a delicate, stylized butterfly with translucent wings held lazily askew. It's called the Lorenz attractor, named for meteorologist Edward N. Lorenz of MIT, who in 1963 discovered this
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 danicamckellar.com  Danica McKellar
From the author of the books for middle school girls, Math Doesn't Suck: How to Survive Middle School Math without Losing Your Mind or Breaking a Nail, Kiss My Math: Showing PreAlgebra Who's Boss, and Girls Get Curves. Read about McKellar's voiceover
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 Daniel Willingham
From the author of Why Don't Students Like School? and When Can You Trust the Experts? (subtitled: "How to tell good science from bad in education"). See, in particular, Willingham's articles, such as "Why transfer is hard," "Why students remember or
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 DapJ Music
Rap music for adolescents struggling to learn and retain math concepts: "Fractions Are Division Problems"; "Keep, Change, Change"; "Properties"; "First, Outer, Inner Last"; and more. The educationally based music production company provides Common Core
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 DareWare: Educational, Multimedia and Java Games
Educational games and multimedia products (free demo versions downloadable), Java games, "This Week in U.S. History", and a brief list of other shareware sites.
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 The Data and Story Library (DASL)
"Dazzle," an online searchable library of datafiles and stories that illustrate the use of basic statistics methods, providing data from a wide variety of topics so that statistics teachers can find realworld examples that will be interesting to their
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 Database of Number Correlations  James Barton
Partitionings, prime factorizations, polygonal numbers, and other data about each of the numbers one through one thousand, as well as connections to "various material and occult phenomena." See also Barton's magic square that has interesting prime factor
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 Data Games  KCP Technologies
As students play Data Games, they generate data that they must analyze to win the games. Supporting materials include a student worksheet; teacher guidelines that correlate the activity to the Common Core State Standards for Mathematics (CCSSM); and videos
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 The Data Library  Pat Daley
Ongoing datasharing projects, downloadable Excel spreadsheets, and other sources of data on the Web. Collaborative Projects  specific data collection projects that teachers and their students may become a part of; Data Sets that can be downloaded as
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 Datamath Calculator Museum  Joerg Woerner
Historical calculators and educational toys, primarily from Texas Instruments. History of calculators, technical details, many interesting sidelights, including downloadable emulators.
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 Data Paint  Man Machine Interface, Inc.
Statistical utility software for for MS windows 95, 98, NT4.0, 2000, that uses GUI (Graphical User Interface) language to link charts, graphs and statistical information about selected groups of data. For each graph and statistics window, there is a corresponding
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 DataStreme Atmosphere  American Meteorological Society
A major precollege teacher enhancement initiative of the American Meteorological Society (AMS). Its main goal is the training of K12 Weather Education Resource Teachers who will promote the teaching of science, mathematics, and technology using weather
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 DAU Math Refresher Tutorial  George Mason University
An interactive tutorial that uses a subway map as a metaphor for moving through the lessons, giving a comprehensive view of basic mathematics, covering arithmetic, fractions, exponents, logarithms, quadratic equations, series, functions, limits, domains
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 Dave's Geometric Pix Gallery  David Joyce; Dept. of Mathematics & Computer Science, Clark University
Mandelbrot and Julia sets, with a generation form and an Explorer on which you can point and click to get more refined images;
Newton Basins and a form to generate them; a page describing tiling the hyperbolic plane; some wallpaper groups; a gallery
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 Dave's Math Tables: Areas, Volumes, Surface Areas  David Manura
Formulas for and diagrams of: areas of polygons (square, rectangle, parallelogram, trapezoid, circle, ellipse, triangles); volumes of polyhedra (cube, rectangular prism, irregular prism, cylinder, pyramid, cone, sphere, ellipsoid); surface area (cube,
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 The David Mulhall Centre  David Mulhall
Site with resources and suggested treatments for people with Dyslexia, Dyscalcula, Dyspraxia and Attention Deficit Disorder. Extensive site, linking to The David Mulhall Centres in London and the UK.
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 Davitily Math Problem Generator  Nguyen, Ly; and Pardue, David
Create worksheets and tests, including options for multiple choice, printable versions, and answer keys. Click to insert preworded questions in basic math, algebra, and geometry, the parameters of which vary randomly. Requires JavaScript. Also available
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 Dear Marilyn, About Leap Years (Math Chat)  Frank Morgan, MAA Online
Your explanation [in Parade Magazine] of September 13, 1998 that we may need to skip a leap year EVERY FEW THOUSAND YEARS because the tropical year (about 365.2422 days) is a bit shorter than the average calendar year (365.2425 days) neglects CHANGES
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 Deberes matemáticas: Ejercicios y problemas de matemáticas resueltos paso a paso.  FORTEC, Formación y Tecnología S.L.
Herramientas didácticas específicas para la enseñanza y el aprendizaje de las matemáticas de la E.S.O. Ejercicios, problemas, exámenes, temarios, todos resueltos y explicados paso a paso. Por suscripción.
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 Decimal Coins of the UK  Tony Clayton
The change to decimal coinage: Decimalisation Day. DDay was February 15th 1971. On that day the United Kingdom changed from the centuries old tradition of using 12 pence to the shilling and 20 shillings to the pound to a new decimal 100 new
pence to
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 Decimal numbers (Middle School Math)  Homeworkhelp.com, Inc.
A lesson on decimals: What is a decimal number? Converting fractions to decimals, and decimals to fractions; Adding and subtracting decimal numbers; Multiplying decimal numbers; Dividing decimal numbers; Rounding.
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 Decimal Places on a Number Line  NASA Lewis Learning Technologies Project
Decimal places: On a number line, which of the following numbers would be the farthest to the right? 0.001, 0.0015, 0.00099, 0.0005. A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Decision Development Corporation
Software for K12 students and teachers, for all platforms. Math software included separately and as part of other product lines. (Gigamath Playground and Junior Gigamath Playground offer word problem practice for ages 714 and 48 respectively; Ellen
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 Decision Making Information  Model Education Systems Associates: MESA, Inc.
MESA specializes in the development, implementation and use of decision support systems and related quantitative information resources, especially quantitative tools for research, evaluation and policy analysis directed toward children and their living
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 Deep in the Jungles  Ivars Peterson (MathTrek)
Humans are predisposed to seeing order and meaning in a world that too often presents random choices and chaotic evidence. Random events sometimes get linked into a meaningful, though ultimately bogus, scenario... At the same time, the mathematics of
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 Deepwater Horizon Incident  The National Oceanic and Atmospheric Administration (NOAA)
NOAA has put together a site full of resources about the Deepwater Horizon oil spill in the Gulf of Mexico. In the left margin, choose "Information for: Students and Teachers" to access data sets as well as articles for the classroom, such as a Q&A that
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 Defining Geometric Formulas (Ask Dr. Math FAQ)  Math Forum
Definitions of two and threedimensional figures in general, and a note on dimensions.
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 The Definitive Four Fours Answer Key  David A. Wheeler
From 0 up to 40,000, whole number mathematical expressions that use only common mathematical symbols and exactly four 4s. Wheeler offers his solutions in three different formats: an abbreviated list of answers; a text file of results, mathematical expressions,
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 Delaware State Data Center  Delaware Economic Development Office
A focal point for the distribution of census information in Delaware and for the dissemination of other information from the federal government, state government and other sources, coordinating the use of census and other data for economic development.
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 Deliberative Discourse Idealized and Realized: Accountable Talk in the Classroom and in Civic Life  Sarah Michaels, Catherine O’Connor, Lauren B. Resnick
An article in PDF format. Abstract: Classroom discussion practices that can lead to reasoned participation by all students are presented and described by the authors. Their research emphasizes the careful orchestration of talk and tasks in academic learning.
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 Demiregular Tessellations  Totally Tessellated
Color renditions and a real example of a demiregular tessellation. Templates allow you to print renditions of each tessellation suitable for coloring activities.
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 The De Morgan Journal  London Mathematical Society
The De Morgan Journal aims "to encourage academic mathematicians to reflect on current issues in mathematics education at all levels, from primary school to graduate studies; to encourage them to explore links between higher mathematics and elementary
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 Demos with Positive Impact  David R. Hill and Lila F. Roberts
A collection of classroom demonstrations that use some form of instructional technology. The authors invite others to submit demos and provide them with feedback on the demos already collected. Demos are organized under the levels of Pre Calculus, Calculus
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 Department of Science & Mathematics Education: Research and Development  Univ. of Melbourne, Australia
Read faculty research and learn about their projects and interests: children's understanding of statistical and probabilistic concepts; the negotiation of meaning in mathematics & science classrooms (The Classroom Project); the expression of algorithms
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 Derek's Daily Math  Derek Orr
"Every Number Has a Story to Tell." This blog by an undergraduate at the University of Pittsburgh details number theoretic properties for every day of the calendar year. Orr, a physics and math major, also maintains a list of "Interesting Propositions/Theorems
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 Desafios Matemáticos  Paulo Ferro
Cinco desafios novos cada mês. Ferro, um professor de matemática licenciado pela Universidade de Coimbra, tambem oferece demonstracões de geometria dinâmica, jogos matemáticos, biografias de matemáticos, exames
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 Descartes 3  Ministry of Education, Culture, and Sport, Spain
Create interactive math lessons in web page format with this applet, or download any of more than 60 already created applets (ranging from "representing numbers on a straight line" to "tables and algebraic terms," from "geometry and a game of billiards"
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 Descartes' Formula (Geometry and the Imagination)  Conway, Doyle, Gilman, Thurston; The Geometry Center
The angle defect at a vertex of a polygon was defined to be the amount by which the sum of the angles at the corners of the faces at that vertex falls short of and the total angle defect of the polyhedron was defined to be what one got when one added
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 Designing a Sustainable Standardsbased Assessment System  Don Burger; Midcontinent Regional Educational Laboratory (McREL)
Designing and implementing a sustainable standardsbased system that consistently yields high student achievement involves more than setting and measuring academic goals. Changing to a standardsbased system provides an
opportunity to reexamine the
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 Designing Effective Professional Development: Lessons from the Eisenhower Program  U.S. Department of Education
The second report of the National Evaluation of the Eisenhower Professional Development Program, Part B (State and Local Activities), a multiyear evaluation being conducted by the American Institutes for Research (AIR) under a contract with the U.S.
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 Designs with Circles  Suzanne Alejandre
A Math Forum Web Unit. Includes some background on circles in Islamic cultures, and an activity exploring the geometry involved in some circle designs.
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 Design Your Future  Math, Science, and Technology for Girls  Autodesk, Inc.
The Design Your Future mission is to provide practical, inspiring, hands
on opportunities for young women to become aware of, explore, and pursue
math, science, and technologybased careers. It provides a number of opportunities, including: a tool
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 Desmos  Desmos Inc
This free online graphing calculator zooms in and out of plots, offers slider bars to explore parameters, switches between Cartesian and polar coordinates, and more. Save sketches, mark points of interest, turn on "projector mode" for thicker, darker
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 Des Trucs et des Maths  Philippe Picart
Sur le nombre pi; le nombre d'or; le Rubik's cube; des ressources à télécharger; et "des trucs de maths divers," comme un JavaScript qui répond à la question "Quel jour de la semaine estu né?" Avec un coins des
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 developer.com's collection of math Java applets  EarthWeb, Inc.
A browsable, searchable collection of links, authors, notes, and details about Java applets contributed to developer.com. Software is organized into the categories of basics and children's, fractals, games and puzzles, general, geometry, plotting, graphing,
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 Developing Algebraic Thinking  Suzanne Alejandre
Teacher lesson plan and student kinesthetic activities on the Traffic Jam activity and applet, as originally published in the inaugural (Fall, 2002) issue of ONMath, an electronic journal of the National Council of Teachers of Mathematics (NCTM).
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 Developing Educational Standards for Schools  Charles Hill; Putnam Valley Schools, New York
An annotated list of sites that have educational standards documents prepared by various states and professional organizations. View standards by subject area or U.S. state. There is a list of state education departments, and resource pages on: U.S. government;
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 Developing Function Sense with SAQs  Judah Schwartz
A work in progress, this is an online book on the philosophy of teaching functions in middle and high school algebra. He has come to believe "that approaching algebra through the study of functions using symbolic and graphical representations simultaneously
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 Diario Fractal  Today´s Fractal  Juan Pablo Braña
A site from Buenos Aires, in English and Spanish, with a different fractal art image every day and archived galleries of past images.
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 Dice and Valentine's Day Symmetries (Math Chat)  Frank Morgan; Christian Science Monitor
A dice challenge from S. H. Logue: The six faces of four dice have these numbers on them: A 1 1 5 5 5 5 B 4 4 4 4 4 4 C 3 3 3 3 7 7 D 2 2 2 6 6 6. You and your opponent each choose one die to use throughout the game. Each round you both roll, and the
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