學生從國小升到國中時，中斷了一年的時間未學習理化課程。當他們進入國二階段後才開始接觸理化課程，密度概念則是學生接觸到的形式操作概念之一，它是無法直接以感官測量或感覺的，它是人們為了說明物體內部所含物質的緊密程度而定義出來的概念，屬於一個二級概念。
本篇研究的主要對象為國中二、三年級的學生，共有322位學生接受密度概念診斷測驗及204位學生接受開放式問卷測驗。主要研究的目的為探討學生對於密度概念的認識與了解的程度。
本研究的主要目的如下：
l.評量國中學生對於密度概念之學習成效；
2.比較不同年級及性別的國中學生對密度概念的認知差異；
3.探討國中學生對於密度相關概念的認知情形；
4.診斷國中學生對於密度概念的學習困難並分析其錯誤概念類型。
本研究採用自行設計的密度概念診斷和開放式問卷的兩種工具。密度概念診斷工具的庫李信度為0.86，內容包括質量、體積、浮力、溫度、狀態改變、比例概念等幾個和密度相關的概念。密度概念開放性問卷則以日常生活及課本中與密度相關的概念來設計題目。
主要研究發現如下：
1.從診斷測驗的結果發現學生對於質量及體積守恆概念或密度基本定義之題目的答對率都有六成以上，但是在密度相關概念的題目之答對率則低於四成。（依主要概念由高到低的答對率排序依次為質量守恆，體積守恆，重量概念，密度恆定，密度比較，重量與密度，體積概念，比例關係，氣體密度，溫度的相關性，體積與密度，浮力）
2.由密度概念診斷的總分之變異數分析得到年級與性別間無交互作用，但在性別上達到統計上的顯著水準 (P<.05)，且男生的總分優於女生，不過國二及國三學生密度概念診斷的總分期無統計上的顯著差異。
3.從測驗結果發現學生對於浮力、體積及溫度與密度的相關性、氣體密度及比例關係等主要概念題型的表現上，其答對率皆低於四成，此結果顯示學生並未建立密度概念與延伸概念之間的關係。
4.從研究結果顯示學生對密度概念的學習困難與錯誤概念之產生原因，主要是學生對密度、體積及質量三者之間的關係未具有正確的了解與認知，而是以公式背誦來代替知識的理解。

Students' acquisitions of scientific knowledge are interrupted when they enroll in junior high schools. In other words, no Physic and Chemistry courses are offered for the students in the first grade of junior high school until they go into second grade level. Density concept is one of the formal concepts in Physical Science. It can not be observed by perception. Rather, it is a concept concerning the degrees of density of the elements in an object. As a result, it is a second-order concept.
This study was to investigate students' understanding of density. The major subjects were the students in the 8th and 9th grade of junior high schools. There were 526 students in junior high schools as the subjects in this research. ( 322 in paper-and-pencil test: 204 in open-ended test)
The purposes of this study were as follows:
1. To evaluate students' learning outcomes.
2. To compare the difference between grade and gender on students' conceptions of density.
3. To discuss students' understanding of the related concepts of density.
4. To diagnose the types of misconceptions and the factors of these misconceptions.
For investigating students' comprehension and misconceptions of density, two instruments were used in this study which included a kind of diagnostic paper-and-pencil test and open-ended test. The content of diagnostic paper-and-pencil test (rKR20 = 0.86) included the concepts of mass, volume, flotation, temperature, phase of change and ratio concept. The original ideas for designing the questions in open-ended test came from the related concepts of density taken from daily life and from textbooks as well.
The major findings of this study were as follows:
1. The percentage of students' correct performances on the conceptions of conservation of mass and volume, and basic knowledge of density was above 60%, but it was lower than 40% on the questions in the related conceptions of density. The order of percentage in correct answers of main concepts from high to low is: conservation of mass, conservation of volume, weight concept, density definition, comparison of density, weight and density, volume concept, ratio, gas density, temperature and density, volume and density, flotation.
2. From the ANOVA analysis for the total score of diagnostic test, there was no interaction effect between grade and gender, but boys got higher scores than those of girls (p<.05). Statistically, there was no significant difference between grade 8 and 9.
3. The percentage of students' correct performances on flotation, relation between volume, temperature and density, gas density and ratio: was lower than 40%. The reasons might be that students could not connect density concept with extensive concepts.
4. According to research Findings, the students' learning difficulties and misconceptions mostly came from the facts that students did not possess a conrect conception among density, volume and mass. Instead, they forced themselves to memorize formula rather than comprehend the conception of density.