Conclusions are WHY we present reasoned arguments.
"Conclusion" has two common meanings. First, a conclusion is the outcome of an argument (which could involve judgment). Second, a conclusion often refers to finality, or ending. The two meanings of "conclusion" are consistent with each other because the outcome typically comes at the end of an argument.
"We reject our measurable hypothesis that students who drink coffee will have significantly greater sprint performance than students who do not drink coffee."
Conclusions can motivate and initiate arguments.
In addition to clearly stating the outcome of an argument, conclusions have an additional role. Having evidence sufficient to support a conclusion is typically what motivates the process of presenting a scientific argument. When scientists are confident that their evidence supports a conclusion, the scientists can begin the process of presenting their research. Therefore, scientific conclusions often perform the function that "claims" serve in more general argumentation frameworks (Toulmin, 1958). Arriving at a reasonable conclusion allows scientists to make a "claim," and begin of the process of constructing written arguments that communicate scientific findings.
Some educational frameworks directly apply the terminology of "claims" to scientific contexts (McNeill, 2008). However, the word "claim" connotes statements that can be made without evidence (e.g. Oxford Living Dictionary). In contrast, conclusions require supporting evidence. "Claims" that remain tentative are commonly termed scientific "hypotheses." However, even hypotheses are typically derived from extensive theoretical or empirical evidence. Therefore, scientists do not commonly use the word "claim" to refer either to hypotheses or conclusions.
Clearly-stated conclusions can both motivate and culminate scientific arguments. Therefore, using conclusions as both topic sentences (at the beginning of arguments) and outcomes (at the end of arguments) can help structure understandable and persuasive reasoning.
Strong reasoned arguments begin and end with strong, clear conclusions. Determining the conclusion (the goal) of an argument before writing can greatly help to develop strong arguments.