Ideas on Increasing School's Interest in Family Literacy & Numeracy Courses

Our funding guidance advises that most of our provision should be used on standard (72 hour+) Literacy and Numeracy Courses.  However, I've found it difficult to find schools who are willing to commit to such long classes.  The main barrier they see is the lack of stable schedules/commitment levels of the learners/participants.  Historically, it's been difficult to keep the same learners in the class all the way through the year - job shifts, family barriers, time commitments, etc. 

Would appreciate any suggestions about overcoming these obstacles and how others have approached the topic, and whether or not it was successful.

Thank you!