I know, I've done all of those things. And sometimes I just count to make sure the silence is long enough for some and not so long that it drives others crazy. But all of these are prayers - petitions and hopes, doubts and praise. If I were to tell you what to do with your silence a number of you would resent the heck out of it. There is too much room for that in the public schools.
Prayer is a voluntary act, as the church is a voluntary organization.
School is not a voluntary organization. Kids have to attend. The best way to diminish a child's desire for a relationship with God is to force one upon them. In the environment of the school, it will feel like an assignment rather than a natural awareness of the soul. It is this kind of spiritual control that drives kids to claim atheism before they have even come to a conscious awareness of God.