The use of bottom-up and top-down processing depends on the context. In some cases, individual words require attention (bottom-up), while in other cases the entire context requires attention (top-down). Bottom – up uses the pieces and breaks down the words individually to understand their meaning before combining the entire read piece. This will sometimes cause a breakdown in understanding because contextual awareness is being used. The top-down approach is more common in classrooms but is not necessarily the most effective approach for reading comprehension. The reader uses the overall theme or purpose to gain understanding. This is sometimes ineffective because individual student variables (race, culture, native language, etc.) cannot place the text in context without knowledge of the individual words. These two approaches combined will be effective in a reading classroom, but may not be effective in a regular educational setting. The approaches place limitations on teachers trying to achieve curricular standards and guidelines. The time factor required to implement these two approaches would be challenging for a normal classroom