The Statistics for your class should be available about 15 minutes after your students finish playing. This time may change depending on the volume hitting our servers. If after waiting a reasonable amount of time (one hour?) and your statistics do not seem to be updating, please contact me at firstname.lastname@example.org.
Note that this is the Statistics in your Teacher Portal and not the "Game Results". The Game Results Page (titled Overall Performance Results) usually gets updated nightly.