Same situation... I just put it in the back of my classroom and explain that I will make them miserable if they mess with it. Also, the first time a class sees my bike I will generally let them look at it and ask me questions about it. That seems to take the mystery away and they do not bother it. While I do not teach 11 year olds(shudder) I do teach middle and high school at an alternative school where approx 80% have been arrested for felonies so they have their own special character traits.....