There are many international and local organisations that arrange voluntary work on regional development projects in Morocco.
They generally pay nothing, sometimes not even providing lodging, and are aimed at young people looking for something different to do for a few weeks over the summer.
Some of these organisations are really just summer camps and international exchange programs. Always ask of the organisation 'who benefits?' Good volunteering projects should be aimed at providing outcomes for beneficiaries not the volunteer.
A good starting point is Lonely Planet's The Big Trip, a guide to gap years and overseas adventures that includes a chapter on volunteering and working overseas, as well as a directory of resources.
International or local organisations that sometimes have Morocco placements or camps:
Chantiers Sociaux Marocains Rabat-based NGO engaged in nationwide health, education and development projects, with international volunteers aged 18 to 35.
Morocco Exchange (www.moroccoexchange.org) Offers short-term student exchange and travel programs with a focus on cross-cultural education through visiting cities and rural villages. Previous custom-made programs have explored Morocco's medical system, the use of the French language, and women's rights.
Peace Corps (www.peacecorps.gov) Long-established US volunteer scheme with deep roots in Morocco; volunteer programs lasting two years.
Idealist.org Has volunteering and job opportunities in Morocco.
Go Abroad (www.goabroad.com) A good place to start looking for volunteer places, as it provides links to organisations with Moroccan programs.
International Cultural Youth Exchange (www.icye.org) Allows you to search for upcoming Moroccan volunteer opportunities.