Unlike most games, Wizard101 has no actual classes. Everyone is a wizard and there isn't any getting around that. What the game does have is schools. What school you choose will effect which spells you can use and for the most part how you will play. There are seven schools of which to be a part, and you can not switch schools at any time. Although you will earn training points every so many levels that can be used to learn spells from other schools. Remember, any spells from your school are free while other schools require training points to learn.
School of Life - Theurgist
The Life School is focused on what the name suggests, life. Those taking part in this school will have the ability to keep others and themselves alive in combat. Their healing abilities limit them when it comes to attack power but they make up for that in accuracy. I'd suggest this to anyone that likes helping others and being in a group quite often. There is always someone that needs to be healed and this is a good way to do it. We also need to take into consideration that you get a unicorn. Who doesn't want a healing unicorn? If that isn't your thing you get to summon a rainbow sliding/gold throwing Leprechaun to attack your enemies. Life Spells get a damage boost from creatures of the Balance and Death schools.
School of Fire - Pyromancer
Fire is generally seen as the main destructive force in games these days but that's not quite the case here. The Fire School teaches spells that will focus mainly on damage over time (or DoT). It is easy to see that the first few spells don't pack a huge punch as you would hope they did but they really build up after a certain point. Taking on strong enemies relies on getting rid of their Health as fast as possible. The ability to stack your spells allows you to get rid of their health at record speeds with minimal health loss on your part. If you have always been a fan of doing damage over time or you just want to get in touch with your inner pyro, this is the School for you. Fire Spells get a Damage Boost against creatures of the Ice School.
School of Storm - Diviner
The Storm School is the power house of all of the Schools. Their spells focus on dealing large amounts of damage to get rid of the enemy quickly. With all that power, they have balancing weakness. The students of the Storm School have less accuracy with their spells as well as less base HP. With great power comes great weakness. If you plan on joining the School of Storm you better be ready to give it your all. One wrong spell could mean your death. This school is suggested for those that want to just obliterate the enemy and don't mind taking harder hits than everyone else. Storm spells get a damage boost against creatures of the Myth School.
School of Ice - Thaumaturge
The Ice School is in general terms the opposite of the Storm School. The Ice school focuses on defense and keeping yourself alive more than taking out your enemies with high damage. Also unlike the Storm School they have the highest base HP, which makes them quite difficult to take down in a short amount of time. This school is great for those that don't mind being the "tank" and in the process sacrificing a little bit of damage to do just that. Their spells also include a fairly interesting variety including an evil snowman. Ice spells get a damage boost against creatures of the Fire School.
School of Balance - Sorcerer
The Balance School is for those that like group play above solo play. This is due to the Balance School teaching students spells related to group play; like buffs. While you aren't quite required to play in a group if you are a member of the Balance School it does focus on that aspect. Having a little bit of everything allows you to be able to attack, heal, and buff yourself. It's the entire concept of having a slight edge over everyone else but at the same time being a tad behind. You should also note the Balance School has no actual building in Ravenwood although you can find the teacher placed near the entrance of it. Balance Spells have no damage boost toward any other school.
School of Death - Necromancer
The Death School teaches the students to "steal and support themselves". They accomplish that through some of their spells having the ability to not only attack their target but have some of that damage be changed into health and given back to the caster. This allows them to heal themselves slightly during combat without having to give up a turn to heal. To counteract this, their spells aren't quite the best in damage, but that's where the buffs come in. This is great for those that just want to be able to do most of the combat alone and don't want to worry about needing or giving support to others. To say that simpler terms: Death School is the school focused on allowing you to play alone. Deaths spells get a damage boost against creatures of the Balance and Life Schools.
School of Myth - Conjurer
The Myth School is exactly what the name suggests, Myth. The schools main focus point is giving students the ability to summon minions that can aid you in combat. Your spells usually involve summoning a mythical creature to attack your enemies for you. Your later spells mostly revolve around getting rid of your enemies defenses and supporting your minions. In the most basic sense of this school it would be classified as the "pet" school. That said if you like having a helping hand to aid in combat this is the best school for you. The Myth School is also a close contender for the "Main Solo School" due to minions being just as good as having a second characters helping you in combat. Myth spells get a damage boost against creatures of the Storm School.