Measure the length and the width of your dresser drawer.
Cut two plywood strips that are as long as your drawer and two plywood strips that are as long as the width of your drawer. These strips should be slightly less wide than your dresser is tall.
Make two marks on one long edge of each strip, spaced evenly to visually divide each strip into three segments.
Make a slit halfway through each plywood strip at the place you marked. Both slits should be made in the same edge of the strip.
Fit the strips together to make a shape like a tic-tac-toe board or a crosshatch symbol. Each slit should fit firmly into another slit, allowing the drawer divider to hold its shape.
Place the assembled strips into the dresser drawer. The stiffness of the plywood will allow the divider to sit upright inside the dresser drawer.