Teaching assistants and science professors grade the discussion section harder than any other part of a lab report. The data table shows what happened, but the discussion proves whether you understand why it happened.
The four-part architecture of an A-grade lab discussion
Part 1. Restate the central objective and principal outcome. Start with a direct summary of your core findings. State whether the experimental data supported, partially supported, or refuted your initial hypothesis, quoting your specific numeric results and percent error.
Part 2. Interpret the data using theoretical mechanisms. Explain the scientific principles that produced your observations. If you observed an exothermic temperature increase, explain the bond-forming chemistry that released thermal energy into the calorimeter.
Part 3. Conduct a rigorous experimental error analysis. Identify specific sources of measurement uncertainty. Calculate your percent error against accepted theoretical literature values and explain why your experimental value drifted higher or lower.
Part 4. Propose realistic, specific experimental improvements. Do not write "be more careful next time." State what equipment, calibration step, or environmental control would reduce standard deviation in future trials.
Replacing "human error" with scientific reasoning
Writing a bare "human error" on a college lab report invites a red pen. It tells the instructor you don’t understand your experimental apparatus. Pin every discrepancy on a specific physical cause instead. One exception. If you know you personally wrecked a step and it changed the outcome, say exactly what you did.
| Never write this | Write this instead | Underlying physical mechanism |
|---|---|---|
| "Results differed due to human error." | "Incomplete thermal insulation of the styrofoam cup allowed ambient heat dissipation." | Systematic heat loss via conduction and convection to laboratory air. |
| "I measured the liquid incorrectly." | "Parallax error reading the meniscus cost us about 0.5 mL on a 100 mL cylinder. Your glassware, your number. Check its least count." | Visual perspective distortion relative to volumetric calibration markings. |
| "The scale was broken." | "Zero-point calibration drift on the electronic balance caused an uncorrected positive tare offset of 0.04 g." | Instrumental calibration offset across sequential gravimetric measurements. |
| "We rushed and spilled some product." | "Mechanical transfer losses during gravity filtration reduced the isolated crystalline yield below the theoretical stoichiometry." | Material retention on quantitative filter paper and beaker sidewalls. |
Example of an effective discussion paragraph
Here is an excerpt from a high scoring physics lab on the acceleration of gravity, stating that "The experimental acceleration due to gravity was determined to be 9.62 +/- 0.14 m/s^2, representing a 1.94% discrepancy from the accepted local value of 9.81 m/s^2. While our measured value falls within two standard deviations of theoretical expectations, the consistently low result suggests a systematic drag bias. Although aerodynamic friction was assumed to be negligible in our theoretical model, the light plastic sphere experienced turbulent air resistance during its 2.0-meter drop, retarding downward acceleration. Utilizing a higher-density lead bob or conducting the drop within a vacuum tube would eliminate atmospheric drag and improve empirical accuracy."
Pre-submission lab report checklist
- Did you compare your experimental values directly against theoretical or literature standards with percent error?
- Did you explicitly state whether the hypothesis was supported or rejected, using your actual numbers?
- Did you swap every bare "human error" for the actual physical cause?
- Are all abbreviations, chemical formulas, and mathematical symbols formatted with proper sub/superscripts?
People also ask
- Can I get an A on a lab report if my experiment yielded the wrong answer?
- Yes. Science experiments often fail due to equipment limitations. Graders reward students who recognize the discrepancy, accurately calculate the percent error, and explain the exact physical mechanism responsible for the deviation.
- What is the difference between the Results and Discussion sections?
- The Results section presents objective data, figures, tables, and calculations with only brief factual explanation of what is shown. The Discussion section explains what those numbers mean, why they occurred, and how they relate to scientific literature.
- Should the discussion be written in past or present tense?
- Use past tense when describing what you observed during the lab session ("The solution changed from blue to clear"). Use present tense when discussing universal scientific principles or permanent literature facts ("Boyle law dictates that pressure is inversely proportional to volume").
References & Authoritative Sources
- [1]Guidelines for Laboratory Reports in Chemistry · American Chemical Society (ACS)
- [2]Writing Lab Reports in Biology and Engineering · MIT Writing and Communication Center
- [3]Writing Lab Reports Guide · Texas A&M University Corpus Christi