A skill class is a method to improve skills by attending one at a rabbit hole in The Sims 3. All skills except Photography, Martial Arts, Nectar Making, and Sculpting have their own class at a rabbit hole. Generally, the standard fee of a skill class is §400, and a class lasts for an hour. This is not always the case; for example, Mixology and Riding classes costs §500 and lasts for two hours, an Advanced Technology class costs §500 and lasts for three hours, and so on.
Sims may attend a skill class between 6 AM and 11 PM. Sims can get a 20% discount by checking the newspaper. However, only pre-Late Night skills and Mixology may have a discount, while the others don't. A celebrity may get another discount[TS3:LN].
Once a Sim starts attending a skill class, they may leave the class and continue later without having to pay an extra fee. Sims cannot attend a class during a concert or a game match at the stadium or a horse competition at the equestrian center, but they can during a bot competition at the plumbot competition arena.
Each Sim may only attend a class of a particular skill once during their lifetime. In addition, they cannot attend a class if they already master the skill, except for Advanced Technology skill. The Advanced Technology skill class is called space training class at the stellar observatory, and attending the class unlocks the moon bounce and commemorate moon landing interactions.