First, note that the scores page only updates every 5 minutes so you might need to wait a few minutes to see the scores come up. If a student completes an assignment, then it should update instantly.
If the score is there, but it seems to be calculating incorrectly, note that the scores are calculated based on the Settings for that student at the last time that lesson or test was worked on.
For example, If they skip the warm-up section, but you haven't turned off the warm-up, it will give them a 0 for those questions.
If you later check the "Skip Warmup" checkbox, the previous scores won't recalculate based on the new settings. This allows you to change the settings throughout their book if you desire without affecting all of their previous scores.
Also, note that Facts Practice scores are kept separate from the lesson and test scores.
If you need to update the lesson or test scores for any previous assignments, you can do that manually by clicking the little pencil icon next to their score on the All Results tab of the reports pages in your parent/teacher dashboard.