STEM toys are made to complement time spent with a parent or teacher, not replace it.

Buying an educational toy for a child is not "the end of a parents’ involvement in how the toy is used and perceived by the child," according to the Association for Psychological Science. "The leader is the lynchpin," according to Jill Berkowicz & Ann Myers, authors of The STEM Shift: A Guide for School Leaders.

Learning through "guided play" isn't a new approach: A UNESCO report from the 1980s explored the use of "Games and Toys in the Teaching of Science and Technology." But, for whatever reason, this method of teaching fell out of favor for many years.

Today, learning-by-playing is an accepted teaching tool, albeit one that is not fully understood, according to the National Association for the Education of Young Children.

A Word About STEM Toys 'For Girls and Boys' "If you want to develop children's physical, cognitive, academic, musical, and artistic skills, toys that are not strongly gender-typed are more likely to do this," according to Judith Elaine Blakemore, a professor of psychology at Purdue University. In other words, the best STEM toys are for everyone -- not girls, not boys -- just kids. Unfortunately, boys are more likely to receive educational toys than girls are, according to an analysis of Amazon reviews published by the American Society for Engineering Education. Boys are also significantly more likely to receive money for college than girls are, according to a T. Rowe Price study. This is a double-standard that parents, grandparents and other adults can break, one gift at a time.

Here are the best inexpensive educational-toys for the money, organized by theme: