Cooperative transmission has been of growing interest recently where users take advantage of each other's resources for better overall performance. In this paper, coded cooperation for wireless networks is considered and a novel cooperative concatenated coding strategy is proposed. In contrast to previous works, this scheme features additional coding benefits other than spatial diversity. Specifically, we show that remarkable error rate reduction can be achieved even when the receive SNR of all cooperating users is maintained at a specific level. The idea of interleaver gain of concatenated codes is exploited and it is shown that the error rate decreases dramatically with the number of cooperating nodes. Multiple cooperating users with unequal message sizes can also be supported easily and a reduced-complexity cooperative encoding structure is provided for good inter-user channels. Code design criteria are also investigated, as well as, the performance under various data-block sizes and number of cooperating users.