This is related to my previous question What value is there in requiring students to declare the dimensions of an answer when it is already clear from context? , but with a different focus.
A sizeable minority of my primary and secondary school teachers (east-coast US in the late 1980's/early 1990's) insisted that word problems be answered in complete sentences.
Consider the following hypothetical question:
Anne's car travels 225 miles in five hours. What is the speed of Anne's car?
The correct answer, according to these teachers, would be
The speed of Anne's car is 45 mph.
Some leeway in wording was allowed, so an answer of "Anne's car has a speed of 45 mph", "45mph is the speed of Anne's car", or "Anne's car travels at a 45mph speed" could be accepted for full credit, but answers such as "45" or even "45 mph" were considered insufficient and would result at best in lost points and at worst in being awarded zero points for the question.
The explanation that I recall being given was that we were being educated to use math to communicate information to others in real-life contexts, and that context was always necessary. For example, if we walked up to an adult and told them "45 mph!", they would look at us like we were crazy and wonder what it is we were trying to communicate, but if we instead presented them with "The speed of Anne's car is 45 mph", they would instead react, "Wow! I've always wondered about that. Thanks!" and would be sure to lavish us with awards and college recommendation letters.
The school system I spent most of my childhood years in was (at that time) very big into interdisciplinary and cross-curricular studies. We were supposed to write papers about math, do math problems on real history, study the history of science, etc., so my understanding was that the requirement to write answers in complete sentences was an exercise in literacy and not mathematics per se.
So, is there mathematical pedagogical value in requiring students to answer word problems in complete sentences, or is this actually a literacy or communication exercise that has been applied interdisciplinarily to math exercises?