The four main mathematical focus points in grade 3 (taken from the Common Core Standards), are:
(1) developing understanding of multiplication and division and strategies for multiplication and division within 100;
(2) developing understanding of fractions, especially unit fractions (fractions with numerator 1);
(3) developing understanding of the structure of rectangular arrays and of area; and
(4) describing and analyzing two-dimensional shapes.
* These are general overviews. For more specific standards, follow the "Common Core Learning Standards" link on the left.