This can happen for a number of reasons. It is possible that too much data is being downloaded from other apps in the background, or that too many apps are open in general. This means that the processor has no way of processing the data from SchoolUpdate. Closing applications in the background and/or clearing the cache of the application or device will help.
It is also possible that the device’s operating system no longer supports the application or that the hardware can no longer process the data.