You can apply for a non Iimmigrant b 90 day visa from your own country under the appropriate work category, you can then Come to Thailand and once you have a work permit (normally assisted by an employer as you need to have a contract of employment, you then can extend your stay for 1 year (not a visa it is an extension of your non b 90 day visa) again the school should assist with that.
I am on a non 0 based on retirement, I arrived on a visa exempt then extended and applied for a non0 based on being over 50, I then extended for 12 months, all done in Thailand and was not too much of a hassle.
I can't comment on consulates as I have never used them.
Tod Daniels you are 100% correct, I spoke to the local office here about work permits, at first they told me I had to find employment, get a contract and fill in all necessary paperwork, leave the country get a non b come back and apply for a work permit.
However another officer butted in and commented I didn't have to do that as each case was based on its own merit, ( however it is easier to obtain a work permit as first pointed out)
I am on a non 0 extension based on being over 50.
When I explained I was living with my gf and in the process of building a house they became quite amiable.
I haven't applied for a permit yet, if and when I do I will update the forum.
I should also point out that I have leased a small 4.3 rai farm, which was the reason I asked about the work permit.