The trial project, which will cost £9m, is funded by the learning council. It is being run in 10 areas and will end in July next year.
If it proves successful, it will be expanded and a further 500,000 workers will be processed in the next seven years.
The project will focus on the on-site assessment and training of construction employees more than 25 years old to NVQ level 2/3. Most of the £9m will be used to help train 275 assessors.
Chief executive of the CITB Peter Lobban said: “Our on-site assessment and training programme is certainly beneficial to companies. Those who want to take advantage should get involved now because there has been a lot of interest and places will go quickly.”
The board said it would it would discriminate in favour of smaller businesses.