What math facts should a 2nd grader know?

Know all sums of two one-digit numbers from memory, and add and subtract within 100.

By the end of 2nd grade

Add and subtract within 20 fluently, using mental strategies, and know all sums of two one-digit numbers from memory. (2.OA.B.2)
Add and subtract within 100 fluently, using place value and the link between addition and subtraction. (2.NBT.B.5)

These come from the Common Core State Standards for Mathematics, which most US states use or have adapted. Your child's school may word them differently.

What that looks like

From memory: 7 + 8 = 15, 9 + 6 = 15, and the subtraction facts that undo them, like 15 − 8 = 7.
Within 100: 47 + 9 as 47 + 10 − 1 = 56.
Subtracting by counting up: 52 − 47 is 3 to get to 50, then 2 more, so 5.

How to practice at home

A few minutes a day works better than a long session once a week.

1-minute addition test (facts within 20)
1-minute subtraction test (facts within 20)
Mental math tricks (add 9)
Mental math tricks (subtract by counting up)

Take the 1-minute addition test

Common questions

How long should my child practice math facts each day?

A few minutes a day is enough for most kids. Short, regular practice sticks better than a long session once a week.

My child still counts on their fingers. Is that a problem?

Counting is a normal step on the way to knowing facts from memory. Strategies like making a 10 bridge the gap, and a 1-minute test shows which facts are still slow.