There are 2 reasons for plants to autoflower. Being cross bred with ruderalis is 1 way. Getting rootbound works for many strains.
With ruderalis you have your Lowryder and its sub progeny. In my opinion, these types of plants yield low because of almost no vegetive period, very leafy bud structures, and I have yet to have pleasant taste or effect from anything with ruderalis mixed into it.
Several strains will autoflower when rootbound, but this is a technique mostly used indoors (mostly). Setting up a proper hole in the ground lined with plastic or somesuch takes some work, but has been done successfully. Also in big plastic above ground containers.
Most strains of cannabis will still rely on 12 hours of light or less to initiate flowering. Many people who want to havest early use some sort of light deprevation technique. Cover the whole greenhouse, bag each individual plant, put them in the pitch black garage at the same time every day.. etc. There are even automated self covering tents available (
http://autoflowertent.com/ ) never used 1, just providing the link
Switch to flowering nutes when the plants begin to show development of flower structures.
If you are to plant in the ground, it is best to ammend or completely replace native soils.
Yields vary according to so many factors it is impossible to estimate. Untill the plant is finished and dried in your hand, you will not know what yield will be, especially if you are running a given strain, seed type or clone for the very first time. Anyone who gives you numbers for this is talking out of thier ass, period.
To stick to your fall timeframe for school and still produce something, an auto flowering strain, some root restriction, and/or light deprovation.... either alone or in combination may be the solution you are after. You should also be able to get flowering times, feeding schedules suggestions etc from the seed supplier specific to the seed you choose.
Good luck in your growing, hope this helps.
YBG
P.S. Here is an old article on the return of ruderalis to breeding for intrest.
http://www.cannabisculture.com/v2/articles/3033.html