How does an 18 year old Thai person learn to ride in order to be able to pass the test for a driver's permit?  Is there a learner's permit category in Thailand?   Otherwise how can they legally practice driving pre permit?  I hope not only on private land.  Thanks 

There is no learners permit...there are some driving schools that can teach car and motorcycle...most just learn with a friend or relative...in a quiet car park or street then when ready goto the local Department of Land Transportation hope to pass then are issued with a "temporary" 2 year licence...which has some restrictions one being a lower allowed alcohol limit

Thank you Johng.  Does the test for the temporary permit require riding the motorbike as with a normal test or is it simply a written test please?

The test incorporates   vision and reaction tests, a computerised road rules theory test,maybe watching a safety video and  then an actual practical driving test...on a mock road which I found the easiest part  some people have trouble with the long straight raised strip about a 30cm wide which you're not supposed to fall off of..I think they recently split it into a two day affair, some offices have long waiting times to get an appointment.