Generally large, typically eight feet by two inches by ten or sixteen or twenty-four inches, sidewalls for modular concrete forms are easily, efficiently and economically produced by cutting and by routing sheet-type polymeric material, preferably polyurethane or expanded polystyrene foam. Metal connecting members are produced in standard sizes by cutting and bending sheet steel and/or wire. The sidewalls and connecting members are transported to a building site tightly and compactly in pieces, and then flexibly assembled into precision wall forms at the site with good efficiency at any scale. The wall forms so assembled define a cavity into which reinforcing steel rod, electrical and/or communications conduit, plumbing, etc., may be entered. Concrete is poured into the cavity to create a wall having the form sidewalls as its permanent surfaces. These surfaces have and present visible, regularly-spaced sheet steel strips suitable to receive and to engage sheet metal screws for mounting anything, including more sheet-type construction materials such as wallboard or paneling, to the wall. The thickness of the concrete wall is predetermined by the dimensions of its metal sidewall-connecting members, and may easily be varied such as during the fabrication of lower to upper wall courses of a multi-story building.