Here is a curated list of free stem worksheets for middle school from Teachers Pay Teachers. All these are free at the time of updating (April 2021). However, some materials may be removed or changed to paid ones over time. I have no control over that, as most of them are not mine.
This resource combines literacy and science. Extra mention for the coloring picture that I find very artistic!
Several fill-in activities about the Sun.
The given grade level distribution is quite wide, I would suggest this for middle school rather than high school. However, clear and useful worksheet about matter.
Word search puzzle about weather and atmosphere.
This material is 55 pages long! I first wondered how this is even possible, but then realized that the publisher is an institute from Australia.
How do we even know that irrational numbers exist in the first place? The crossword can be used as summary after the irrational numbers course.
Long and engaging material about cells. Pictures are colorful and tasks varying in style. This pdf version is free, the e-learning version is paid.
A video guide about quarks and leptons. Refers to several short videos, a good way of presenting these complicated structures. It’s for classes 8-10.
This fieldtrip has several virtual materials (videos, 3D environment), answer sheets with pictures, grading rubric. This virtual field trip has it all (except juice boxes)!
This material is a video and worksheet combo about meiosis.
Large unit for Google Drive about Electrical energy. First there is the theory, then a quiz.
Hopefully you will find these materials useful!