I believe that most of the rules that exist between employees and their employers are not stated in contracts or laws, but are not written and sometimes even not spoken (i.e. implicit). This is natural and does not imply that you are in a toxic work environment. However, "your presence is really important" is just an example of doublespeak.
It is likely that your contract protects you from being fired or punished in case you don't comply with this kind of request. However, this is far from being a decisive answer.
If you don't comply with the demands of your employee (regardless they are stated in the contract or not), you may miss the rewards and/or career advancements you deserve, unless you manage to carry out some form of moral suasion towards your employer (using your negotiation skills) or reach consensus among many of your peers (beware: this is an aggressive strategy, it is not necessary in most cases, and is very risky!).
I suggest you to go to this event for this time asking some of your "schoolmates" to take notes for you. Then, provide your employer with the schedule of your classes kindly asking to minimize, if possible, the collisions with the extra-hours they require you. Do remark that this is very important for you and will affect your performance at work making you a "more educated, satisfied, and self-confident individual". If collisions continue to happen all the times, try to find a trade-off (say 50-50) between school and work, by constantly probing the mood of your employer. Adapt the trade-off by favoring school or work as needed. And last, when you go to these events, make sure you are not invisible (this does not mean you have to be a lap dog but at least don't hide under some table or stay alone in a corner, like "I don't want to be here").