Blackboards rhymes with:
baseboards, billboard's, billboards, cardboards, checkerboards, chessboards, clapboards, dashboards, floorboards, headboards, keyboards, outboard's, outboards, pegboards, snowboards, surfboards, switchboards
baseboards, billboard's, billboards, cardboards, checkerboards, chessboards, clapboards, dashboards, floorboards, headboards, keyboards, outboard's, outboards, pegboards, snowboards, surfboards, switchboards