If a piece of writing requires research, you need to estimate that separately. Typical industrial productivity has been reported as 8-20 debugged, documented, delivered lines of code per working day. Students are also spending a lot of time learning the quirks of their programming languages and tools. The mix of activities in a student program is different from an industrial setting. A typical programming assignment has very little requirements analysis, little or no architectural design, and only small amounts of detailed design.
Testing is usually much less rigorous than in industry.
I would be delighted if anyone can point me to validated numbers.