Abstract: A space-dividing wall panel system having a plurality of upright wall panels serially connected one with the other by an intermediate upright support post. The height of each wall panel is adjusted by modular panel extension assemblies which are mounted on base panels supported by lower support posts and include extension posts connected to the lower support posts so as to be arranged coaxial therewith. Spaced apart pairs of the extension posts are connectable to a cross rail at upper ends thereof which defines a downwardly extending generally U-shaped extension frame. A serially adjacent pair of extension frames shares a common extension post which is connected to both of the cross rails thereof, where the base panel and the extension panel assembly disposed thereon respectively define base and beltline raceways for workstation cabling. Additional extension posts can be inserted into the upper ends of extension posts already positioned so as to vertically extend the height of the wall panel.