This activity is for practicing comparative grammar, specifically adjectives that end in -er and the "as ---- as" pattern.
First, I explain with an example. I write the sentence "I am taller than ---------" and look around the classroom. When I find a short student, I ask them to stand up and make a show of comparing our heights. If you're trying this, you probably want to pick a student that doesn't seem very self-conscious about their height. I go back to the blackboard and write the student's name in the blank.
Next, I write "I am shorter than -------." underneath and go searching around the classroom for a tall student. Once I find them, I compare our heights (kneeling down a little if I have to, just to get the point across) and then write their name on the blackboard as well. Finally, in between those two sentences, I write "I am as tall as --------." and set out to find a student of roughly the same height.
I go through the process again with the next set of sentences on the worksheet where I try to find a student with longer hair, shorter hair, and hair that's about as long as mine. Once I confirm that the students understand the sentences I wrote, I pass out the worksheet and ask them to search for classmates that they can write in the blanks. Unless it's a very small class, I tell them they can write a classmate's name only one time. It might be good to review the spelling of the word "heavier" before you start.
After about 10 or 15 minutes, I call time and ask everyone to sit down again. This last step is optional. Each sentence has a letter next to it: A, B, C, or D. Students should write how many sentences they wrote in the "A" category, how many in "B", and so on, and then multiply them by the number for each category. Then they total them up to get their final score. I just have a score to give a fun extra step that makes it feel a little more like a game, but if you use any kind of class rewards like points or stickers, you can tie it to that if you want. I print the score sheet on the back of the paper, but you can leave it out if you don't feel it's necessary.