There are 11 levels of addition math timings. They are leveled 0 to 10. Each timing has 20 math facts. Students must answer ALL facts correctly in 1 minute to move on to the next level. All math facts on level 0 are +0 problems. Half of the math facts on level 1 are +1 problems and the other half are review (+0's) and so on.
Example: Half of the math facts on level 7 would be +7 facts. The other half would be review problems from the previous levels (+0, +1, +2, +3, +4, +5, and +6) That way students are mainly practicing the +7 facts, but also reviewing other facts.
(I also have subtraction, multiplication, and division timings, as well as a cover booklet that we use at our school to keep track of each student's level.)