I co-signed a lesae with my son, for a room in the who is a student in January of 07 for a lease period Jan 07 - Aug 07. The landlord then contacted the students later that month and said if they wanted the house for the following school year they had to sign a lease alteration, which my son did for lease period Aug 07 - Aug 08. I was never contacted as the cosinger for my signature on this alteration. I have a copy of the alteratiion, which has a place on it for my signature, but is unsigned. My son is not returing to school and I need to know what my rights are on the alteration, is it valid without my signature or do I have the right to fight that the lease for my son terminated in Aug 07

It depends on how its worded, but frankly I don't think you have much of a case. A co-signer on a lease is generally a guarantor, not a party to the lease. This means they could be made to pay if the tenant defaults.

If your son signed an EXTENSION of the lease to Aug 08, then he is bound by it, but you are not. Even if the lease was amended to change the expiration, it would probably relieve you for responsibility as gurantor, but not your son for responsibility for the term.