As Pitarou says, the workshop advice makes sense only in the context of a longer piece of writing. It does not apply at the sentence level.
A common way of organising a persuasive essay is to include the conclusion in the introduction, and then to spend the rest of the essay supporting that conclusion. The common term for the "conclusion in the introduction" is thesis statement, which is usually the last sentence of the introduction.
Expository or analytical essays also typically include in the introduction some kind of brief summary of material to be covered in the body. This may or may not be referred to as the thesis statement. Sometimes this summary will include a conclusion and sometimes the conclusion will be drawn only in the final paragraph.
How you organize any given piece of writing should be determined by the typical rhetorical patterns for that genre in your field. So attentive reading of examples in that genre is probably more useful than generic advice from a workshop.
OWL at Purdue is a very good source of writing advice in the various genres.