Forming systems and assemblies as disclosed herein comprise a composite material comprising a structural component and a resin component combined with the reinforcing component. A forming element is disposed within the composite material and has a coefficient of thermal expansion that is greater than that of the composite material. The forming element is positioned to provide a desired integral structural reinforcement and/or surface feature to the composite. The composite material may comprise one or more passages extending from a surface thereof to the forming element. The composite material may be cured by heat to take a set configuration and then allowed to cool. The cooling of the composite material and the forming element enables the forming element to contract relative to the composite material and become delaminated therefrom to facilitate easy removal, and thereby provide an improved method and assembly for making structural reinforcing features in composite structures.