I know there are people who would like to be able to search the activities by grade level and at one point I thought about adding labels along those lines.
But then I realized those labels wouldn't do much to narrow down your search, as I'm a firm believer that the bulk of the activities I share can (and should) be done with a very wide range of students.
Let me give you a few examples...
I originally learned the Heart Mambo at a Life Science Institute for middle school science teachers I attended. In its original form, it is clearly meant for 7th grade (give or take...) students to learn the path the blood takes through the circulatory system, with a fair amount of detail (names of the specific arteries and veins through which the blood passes at each point in the cycle).
A few years later, I was asked to provide a science activity for my son's preschool class as part of their study of body systems, particularly the heart. I used the same premise, but greatly simplified things.... There was a large heart in the middle and two loops - one going to the lungs and the other going to the body. They walked the loop and named the places they were passing through. In addition, I had them pick up construction paper oxygen molecules at the lung and deposit them at the body.
And while I haven't had opportunity to work with older students, I think plenty of them would enjoy the addition of some kinesthetic activity to their reading and lectures. I would anticipate adding additional pieces of information, such as the valves.
A really, really simple activity is the Sticky Web. Totally appropriate for students as young as preschool learning about spiders and their webs.
But... I did the exact same activity, without any modifications, with my middle school students. It took less than 5 minutes, but it was hands-on and got them involved. And it doesn't even matter if they'd done it before - each time they do something they get something different out of the experience, based on their accumulated knowledge up to that point.
I encourage you to find ways to use these activities to meet the needs of your students and your situation. If you see something you'd like to use and aren't sure how to adapt it to your situation, shoot me a message and we can brainstorm together. Also, if you're looking for activities that you can use to teach a particular skill (as opposed to a content area), let me know and I'll try to lend a hand with that as well.