Report Abuse. 1  Learn How To Do Fractions. 2  Kids get only basic instruction in fractions in elementary grades. 3  kids start learning fractions between 3rd and 4th grade.  I believe more like the 5th grade; however possibly 4th 1  grade. 4th Grade You basically have easy questions like identifying a problem. 5th Grade you add and subtract common denominators and unlike denominators finding and identifiying what a real fraction. 6th Grade you start to add and subtract unlike and common denominators by mixed numbers using various numbers. 7th Grade You do all the same stuff in 4th - 6th Grade But you start learning about proportions which is missing numbers finding x is common.