I'm travelling to Thailand at the start of March to do 12 weeks of voluntary English teaching.I then plan on travelling around Thailand and SE Asia for about 2 months.While I am working I will have a Non-Immigrant "B" visa,which will last 90 days.My question is: will I be required to show evidence of onward travel either by Thai immigration or my airline (SAS)?I am flying from Dublin and have a return ticket booked for late July.I not plan on overstaying this visa,as I am on the Laos border.

If you have B-visa issued by a Thai Embassy or consulate abroad, one does not need an outbound ticket.

Why not apply for a multiple entry visa ?   The Thai Consulate in Dublin is very friendly ......that eliminates any problems and lets you leave and return at leisure. If you have a single entry Non B visa and make a visit to Laos that visa is at an end.