There are dozens of websites with free educational clipart for students and teachers. One of the most popular sites for these images listed on LearningReviews.com is Clipart for Free.
Clipart for Free is a blog site with category links to a broad variety of themes. The images are free for personal use and ideal for homework projects. This is mainly children's clipart for elementary age students because of the clipart's cartoon quality, but older students will find useful ones there as well.
The clipart collections include animals, sports, holidays, teddy bears, and seasonal clipart of spring, summer, winter and fall. Other clipart themes include religion, cultures, food, patriotic, weather and nature.
The anonymous author adds new images up to several times a month, so check the site occasionally for a new find.
Looking for more school-related clipart? You'll find detailed descriptions and links to two dozen of the best school clipart collections I've seen in the Educational Clipart section of LearningReviews.com. The broad range of themes for students of all ages includes back to school, math, science, history, reading and writing. Some of the sites request attribution if you use their images on a classroom website, blog or wiki.