This is very important as far as understanding this number system is concerned, if not re-enforced with the help of some visible and tangible objects it will appear difficult to the learners. To help students comprehend this concept the first and foremost teaching aid would be a number chart "hundreds/tens/ones". Once the student is taught to place numbers in this manner the concept becomes simple and students remember it life-long.
At this stage the teacher needs to remember that the class room has students with different needs and capabilities therefore a good lesson should be rendered with the average student in mind .Teacher may use worksheets with number chart on it and ask students to place given numbers in various combinations. They can be written on the worksheet and also read out in class. This method will re-enforce student learning further. Sometimes number blocks help specially students who need special attention, because actually holding a number block in hand helps in concretizing the concept.