When we want to describe a good day at school, there are several synonyms that we can use. One of the most common is 'successful day' since it implies that the student accomplished their goals for the day. Another great option is 'productive day', which means that the student was able to complete all of their work and make progress towards their academic goals. 'Fruitful day' is another synonym that can be used, as it suggests that the student learned valuable lessons and was able to use them to their advantage. Lastly, 'excellent day' can be used to describe a day that was exceptional in terms of academic success, positive learning experiences and overall happiness.