We developed running water experiments based on the selective transport hypothesis to teach downstream grain-size changes in fluvial sediments. We conducted the experiments using a channel with a curved, gentle slope. Eight experiments were carried out by changing the water supply rate （9.5 mL/s or 16.8 mL/s） and the types of samples used （pebbles or granules, medium or fine sand, and mud）. Two experiments showed sediment distribution, which clearly indicated gravels in the uppermost stream, sand in the upstream to midstream, and mud or sandy mud in the downstream. Both were conducted with a water supply rate of 9.5 mL/s, one using pebbles, medium sand, and mud, and one with pebbles, fine sand, and mud. We conclude that the experiments can instruct on the downstream changes in grain size in fluvial sediments.