Full Idea
The class which has the means of material production at its disposal, has control at the same time over the means of mental production.
Gist of Idea
The class controlling material production also controls mental production
Source
K Marx / F Engels (The German Ideology [1846], §1.B)
Book Reference
Marx,K./Engels,F.: 'The German Ideology', ed/tr. Arthur,C.J. [Lawrence and Wishart 1985], p.64
A Reaction
This is mostly true, because the wealthy will control both the media and most of the educational institutions, but in a world of universal education and underground presses it doesn't seem to be a necessary truth. Wide dissemination of ideas needs money.