The impact of fastener type (glued and unglued butterfly dovetail keys, glued and unglued H-shaped dovetail keys, one-pin dowel, two-pin dowels, and plywood spline) and wood composite material type on the bending moment capacity of L-shaped mitered frame joints under diagonal tension and compression loads was investigated. Specimens were constructed of laminated medium-density fiberboard (LamMDF) and laminated particleboard (LamPB). The glued joint specimens were constructed with polyvinyl acetate (PVAc) adhesive. In both tests, joints reinforced with two dowels had the highest bending moment capacity, whereas unglued joints fastened with H-shaped dovetail keys had the lowest capacity. Splined joints were characterized by the second highest bending moment capacity. Two-pin dowel joints had, on average, 47% greater capacity than one-pin dowel joints. The glued dovetail joints were 31% stronger than the unglued joints. There was no statistically significant difference between the bending moment capacities of butterfly and H-shaped dovetail keys. The LamMDF joints exhibited 7.8% greater capacity than joints constructed of LamPB. Overall, the bending moment capacity of joints loaded in compression was 22% higher than that of joints loaded in tension-when the moment arm in the compression specimens was taken at the inside corner of the joint.