Here is a list of free first grade math worksheets aligned with the common core standards.
Fact Families to 12 - Graphic Organized Facts
Counting to 20 - Fill in the Missing Blanks
Counting: What Comes Before and What Comes After?
Count by 5s
Count By 10s
Counting By 2's
Adding(For 1st grade adding is only to 20 without re-grouping/carrying)
Greater than or less than to 20
Order the numbers to 50, smallest to largest
Telling Time Worksheets(Some of these are 2nd grade)
Subtraction(For 1st grade subtraction is only to 15 without re-grouping/carrying)
Hundreds Chart Worksheets
More Word Problems
Counting Pennies (US, Canadian and Generic Pennies)
Counting US coins to 50 cents
Counting Canadian coins to 50 cents
Addition Sentences to 10
Ordinal Numbers to 10(First, second etc.)
Adding to 10
Adding to 15
Adding to 20
How Many More to 10
Fill in the Missing Numbers - to 10
How many less - to 10
Subtraction Facts to 10
Geometry: Shape Book
10 Geometry Worksheets for late Kindergarten and Grade 1
Beginning Fractions: Concept of 1/2.
When working with first grade students, it's important to start from where they are at. It is also important to focus on thinking concepts. For instance, think about this word problem:
A man has 10 balloons and the wind blew 4 away. How many are left.
A man was holding some balloons and the wind blew 4 away. He only has 6 balloons left, how many did he start with.
Too often we ask questions where the unknown is at the end of the question, start puting the unknown at the beginning or at the ending of the question.