As a little warm up on the maths lesson you can do this little exercise as I did today in grade 5. Think I got the tip from Margareta Forsbäck. It can be adapted for use in all grades. Begin by distributing the paper in which students write a big equal sign on one side and a crossed out an equation on the other side.
Then, put statements on the board, like 0.2 2/10 or 1/2 6/3 and let the students show up right sign. The class is immediately activated and hopefully even the rest of the lesson.