Todo Math for the Classroom is engineered to automatically sync students' progress to your Teacher Dashboard any time the play device is connected to WiFi. Play data will sync any time a game is completed, so as soon as a student completes a game (and the device is connected to the WiFi network), the progress will automatically show up on your dashboard. If the device isn't connected to WiFi, it will sync the next time that it is connected.
You can also sync manually. Just open the app, go to the Teacher page and tap "Sync" on the right side of the screen — again, you'll need to be connected to WiFi to do this.
If progress is failing to sync, the issue is often related to the WiFi connection — double check that your device has WiFi bars and that you're signed in to your network before using the app. If this still doesn't work, check your device's settings to make sure that Todo Math is not prevented from accessing the internet — a connection is needed to sync progress.