doing for him is work-for-hire. In the agreement you give the publisher full ownership and
control of the material. You would not be allowed to sell reprints or to use the same content at any time in the future. This is different from all rights in that with all rights, the rights will automatically revert to you after 35 years. Not so with work for hire. If you are selling a piece to a publication as a freelance writer, that does not qualify as a work for hire. Typically, writing can be considered work for hire when it has been created as part of the job you do for your employer. What you write in that situation belongs to the employer.
However, there are a few legitimate situations in which you may be asked to sign a work-for-hire agreement in connection with a writing assignment you are given. One example might be if you write Sunday school curriculum. Because such material is used in multi-year cycles, the publisher needs to be able to reuse it in the future without having to go back to the writers for permission. In such a case, signing the work-for-hire contract is legitimate—especially since it is not something you could sell elsewhere anyway.
If a publisher asks you to sign a work-for-hire contract on a piece you submit, or even one you write on assignment, you need to challenge them. In most cases, if challenged, they will back down.
To see a sample of a work-for-hire agreement, go to: http://www.vlaa.org/assets/documents/Sample%20Work-For-Hire%20Agreement.pdf.