Last year, I introduced Op Art to my 3rd grade students, and taught them Mr. E's 3D line design. I had a very talented group that year (they are my current 4th graders, and still achieving beyond grade level in art for the most part), and their line designs turned out very well.
This year, I tried the project with an older group: my 5th grade students! They get a little restless toward the end of the school year, so a project that begins with following a few simple steps keeps them a little more focused. Also, I didn't know if we'd have time to finish one more art project before the end of the school year, so I chose this assignment because they can finish at home on their own if they want to. If I'm going to send home an unfinished art project with my students, I'd like them to at least have the option to do it on their own! Also, I think these designs still look cool when they're only half-way colored.
An added tool I had to teach the lesson this year is my Promethean board! It was so easy to teach each step by drawing on the big board with my Promethean pen. All the students could see clearly, and I could demonstrate "mistakes" and erase them effortlessly so the students would know what not to do before even picking up a Sharpie!