We tape the end of our weft string to the center of our plate, under the warp strings. I stress to them to make sure to weave along the edge of the plate where it is very clear what warp string comes next. These first few steps can make some fifth grader's head spin and they struggle to work through them. But as soon as they weave around the plate a couple of times they remember from their previous experience and they even think the circle is easier than the rectangle.
I remind them not to pull tightly as they go around or they could end up with a bowl shape or the ends of the weaving curl up. When the plate is full, we flip it over and cut the warp strings and remove them from the cuts along the edge of the plate. The warp strings are knotted gently to avoid curling. They may then leave their warp string long or trim them.