If you could find a duplex property (or a single family house that could be turned into a duplex--check any HOA restrictions first), or a "fixer upper" to live in, that could be a better use of the equity you have in the rental house.If you run the numbers and decide it makes sense to sell the rental house (check with your accountant, figure out closing costs to selling and buying) then you'll possibly have more money to put towards a primary residence.You may want to check the neighborhoods that fall in the school district you want to stay in and look in "under appreciated" areas...maybe not the A class neighborhoods, but ones that have potential of becoming "improved".While I understand your desire to stay in a particular school district, it's not the end of the world to consider other districts if they will allow you to build real estate/family wealth that will put your entire family tree in a better position."

This is where I struggled when my income was very low. 

Depends on the exact scenario but could be as low as high 6's with prepayment penalties. 

Quote from @Bonnie Low: If you're interested in the MTR strategy, I invite you to participate in THE MTR Connect.

Any ideas on cost per square foot?  

If she leaves September 15 and the new tenant doesn't start until October 1, then you can hold her responsible for rent, utilities, and other costs through September 30th.Don't wait for problems to happen before developing a plan.

And ideally sell it 4 years later.If I can more or less count on the renting of additional bedrooms to cover the running costs of the house, I'm really only looking at taking a hit on the buying/selling costs - which SHOULD be lower than what it would cost to house him in dorms for 4 years.I feel like this is pretty obvious and easy (not trying to make significant money here, just thinking I could save $10-$20k on housing costs over 4 years).

I cleared $10k on my first one.We ended up clearing $30k on the second one.The last flip was very stressful for my wife and she wants to keep our finances (HELOC) out of the next one.I am going to look to find a financing partner to cover the carrying costs of the next flip.On a $400k house (average for my area), the total investment would be $85-$95k and would be paid directly to the lender and subs/suppliers, not to me.I can bring the lender, as I have a good rep with the one I use.I will do all the rest.

This Water Street property in Delphi, IN, was an attractive investment due to its low purchase price of $21,000 and the potential for significant value addition through targeted renovations.

Diversify your study by including communities with employment growth, schools, and low crime rates.