A thermosetting composition that includes a co-reactable solid, particulate mixture of a film forming material having functional groups and a crosslinking agent having at least two functional groups that are reactive with the functional groups in the film forming material. The crosslinking agent includes a copolymer having at least 30 mol % of alternating structural units of a residue from a donor monomer and a residue from one or more acrylic acceptor monomers. The thermosetting composition may coat a substrate by coalescing the composition to form a continuous film and curing the composition. The thermosetting composition may be included as part of a multi-component composite coating composition that includes an optional primer coat, a base coat deposited from a pigmented film-forming composition, and a transparent top coat applied over the base coat, where either the base coat, the transparent top coat, or both, are deposited from the thermosetting composition.