Topic sentences and units of support need to be ordered consciously in your essay draft. There may be multiple ways to order your topic sentences and units of support for the same thesis and you, as the writer, need to identify an order that makes sense, given your purpose, content, and reading audience. Here’s an example:

Thesis: The first five years and the use of age-appropriate strategies during this time are the most critical to successful language development in children.

Possible Order #1: Your research may have uncovered that there are general stages related to each year from one to five. Your purpose is to argue for the importance of particular stimuli appropriate for each year, in order to facilitate language development. You decide to order your topic sentences and units of support chronologically, year by year.

Possible Order #2: You’re writing an essay based on personal observation, with the purpose of arguing for the implementation of certain strategies for fostering language development during this entire period. You decide to order your topic sentences and units of support strategy by strategy. Additionally, you decide to either order your topic sentences and units of support from most to least important, or least to most important, depending on what you think will best retain the interest of your reading audience.

Possible Order #3: You consulted the Child Development Institute website and learned that there are four components to language: phonology, semantics, grammar, and pragmatics. You decide to order your topic sentences and units of support using these categories, which are also presented in an overall chronological order based on how children usually learn, in order to logically argue to a general audience that there are strategies that can successfully foster these components.   (https://childdevelopmentinfo.com/child-development/language_development/#.WrPVZ-jwY2w).

It doesn’t matter if you develop your topic sentences and units of support as an outline, before you write a draft, or if they emerge as you write a draft. The point is that, once you have topic sentences and units of support that relate to your working thesis, you need to consider their order in the essay, so that they exist in some type of logical sequence.