Abstract: Side rail assemblies for beds are generally discussed herein with particular discussions extended to adjustable side rail assemblies. The side rail assemblies discussed herein have an under-mount frame support for supporting a brace member, which has a coupling assembly for coupling a rail guard to the brace member, and hence to the under-mount frame support. The rail guard is movable to a non-blocking position to permit ingress and egress to a bed and to a blocking position to limit ingress and egress to the bed. In the blocking position, the rail guard may be used by a user to upright himself or herself from a lying position.