Creative Commons – Which License?

Creative Commons – Which License?:

Please help me choose…
…which Creative Commons license should I put on my sites.
There are only five choices but they are proving difficult. They are as follows:
COMMERCIAL USES

http://creativecommons.org/choose/

Yes means:

“Commercial Use – The licensor permits others to copy, distribute, display, and perform the work, including for commercial purposes.”

Does this mean others can sell my lessons? (which I do not want as I provide them for free.)
No means:

“Non-Commercial – The licensor permits others to copy, distribute, display, and perform the work for non-commercial purposes only.”

Does this mean language schools cannot print them and use them in class (provided my URL is on each page). Naturally, I want schools to use them.
Neither choice seems ideal.
MODIFICATIONS

http://creativecommons.org/choose/

Yes means:

“Allow Derivative Works – The licensor permits others to copy, distribute, display and perform the work, as well as make derivative works based on it.”

The middle choice means:

“Share Alike – The licensor permits others to distribute derivative works only under the same license or one compatible with the one that governs the licensor’s work.”

No means:

“No Derivative Works – The licensor permits others to copy, distribute and transmit only unaltered copies of the work — not derivative works based on it.”

Do I want others to make derivative (altered) copies of my materials?
All help / suggestions appreciated regarding the pros and cons of the above five choices.
Thank you

Sean