Decimals

Decimals are understood as so many units of 0.1, and addition and subtraction are carried out in column form. The work extends to cases that carry and borrow, and Fill in the Blank plus word problems such as Addition (Comparing) and Subtraction (Comparing) tie each situation to an expression.

Lining up the right-hand ends in the column instead of the decimal points is the standout error, turning 2.5 + 13 into something like 3.8. Check whether the decimal points sit in a straight line. Presentation trips children up too, as when 1.0 is not rewritten as 1, or 0.5 is written as .5.

The procedure of lining digits up by place, learned in Column Subtraction, is replaced here by lining numbers up against the decimal point. Once the way decimals are written feels familiar, the very next unit, Decimal Units (Capacity and Length), puts it to use rewriting capacity and length.