General recommendations:
Alternate algorithms

Estimation
Mental math

Problem solving

Venn diagrams

"Add to" problems
"Take from" problems
"Put together / take apart" problems (PTTA)
"Compare" problems

Level 1: Direct modeling strategies
Level 2: Counting strategies
Level 3: Decompose / recompose

Equal groups

Remainders

Multiplication with arrays/area

Multiplicative comparisons

Numbers and place value

Arithmetic

Error patterns (aka. buggy algorithms)

Integer models

Prime factorization

Properties of operations
