Remember to make the best of what is already provided in the Investigations materials. The Ten-Minute-Math routines and games are great for helping students learn their basic facts. When I first became involved with the program, I was involved in a special pilot with just Title I children. At the beginning of the year, I gave the group of second grade children a sheet of 100 addition facts and up to 10 minutes to complete the page. Dan could only complete 22 problems correctly, but by October he could do all 100 in 3 minutes and score a 100%. When he returned to a regular third grade classroom the next year, and the same 100 facts were given to the class, he could still do them in 3 minutes and score a 100%. Several of the other students in the class, including those that we often label as gifted/talented were counting on fingers. When the time was up, Dan replied, "What was so hard about that? Didn't you guy learn how to think last year?"
This is what it's all about - helping the students learn how to think. Ten's Go Fish, Turn Over Ten, Close to 20, Beat the Calculator are great for providing opportunities for the children to do just that. We played the games every Friday and by October, most all of the students could complete the facts in five minutes or less. Remember, these were ALL Title I students. The key is the questions I asked the students as they played and the reflection we did each time. It's also important to have them record the combinations they make. For example when playing Tens Go Fish: If I ask Judy for a 6, what number does that tell you I must have in my hand? How do you know? If I have a 7 in my hand, what number should I ask for? Once the children learn the combinations of 10, the rest of the facts are simply a matter of place value. If I know 8 + 2 = 10 then 8 + 6 = (8 + 2 from the 6 to make a ten and then four left over. 10 + 4 = 14) There are lots of supplemental resources available, but I think the games with good questioning from the teacher, is the best thing I've seen get great results with the children.
There is a literature connection by Greg Tang - The Best of Times, that is great for teaching thinking strategies for learning multiplication facts.
Nimble with Number, published by Dale Seymour, is also a great series of sponge activities and practice pages.