In non-Montessori environments, the tendency is to push towards minimal planning. In this way, the children are not given too much, too fast; parents and teachers do not feel "overwhelmed" if the plans weren't completed in a set timeframe (because now we need to move on to the new set of weekly plans, i.e. in an environment that centers on weekly themes).
In Montessori we over-plan so that we are always prepared to meet a
child's interests and needs.
Elementary: We don't know which presentation is going to incite a deep interest, so we present and present and present until something clicks - and then they are off. And we might not then present something new for several days - or we'll still drop little plant stories here and there for example, or recall a language-deep child back to geometry with a story about Pythagoras - just to keep it fresh.
The albums are not necessarily the easiest to organize by ages, because of the wide differences from one child to the next, but it is possible to focus on the most likely possibilities for one year at a time.
Primary: We prepare ahead, but know that we will present and back-off. I love how primary albums can be reorganized into groups of 6 month spans. Within those 6 months, the child has a lot of space to explore but the adult can better focus for planning purposes.
But we also have to balance that over-planning with the recognition that a child's interests might take off and we set aside our plans for a time. Therefore *our* plans have no date on them. The elementary child's work-plan might have dates, and there is where we help to work through the planning process of what MUST be done within a time-frame and what can be put off while a new interest is being explored.