See also Monolingual dictionaries vs bilingual dictionaries
Rubin (1975) states that "the good language learner is a willing and accurate guesser".
Benoussan, Sim and Weiss (1984) found no correlation between dictionary use and reading comprehension scores of EFL/university students.
Hosenfeld (1984) prompts teachers to train learners in the use of guessing techniques, so that they can avoid the dictionary.
Carrell, Devine, & Eskey (1988) believe that L2 learners should consult a dictionary sparingly and only as a last resort.
Tono (1988) found positive correlation between dictionary skills and reading comprehension scores.
Summers (1988) Results suggest positive correlation between dictionary use and reading comprehension scores.
Neubach and Cohen (1988) Dictionary did not help much in reading comprehension of EFL/university students.
Laufer (2005) estimates that vocabulary learning from context is only possible and reliable when the student understands between 95% and 98% of the text.
Luppescu and Day (1993) suggest that the dictionary use can have a positive effect on vocabulary acquisition.
Hulstijn (1993) EFL /Y 10-11 students with larger vocabularies looked up fewer words than subjects with smaller vocabularies. High inferring ability need not result in less dictionary use than low inferring ability.
Cho and Krashen (1994) in the Sweet Valley studies found out that, of the four test subjects, the two who used the dictionary learned more vocabulary per words read. The authors still wonder whether the time spent with the dictionary was well spent. An overview of free voluntary reading studies, controversies etc. can be found here.
Knight (1994) found that university students who used dictionaries learned more words but also achieved higher reading comprehension scores than those who guessed from context. The negative point in the use of the dictionary was the reading rate.
Hulstijn, Hollander and Greidanus (1996) found out that when a student looked up a word in the dictionary, their retention rate was higher than other reading conditions such as marginal glosses.
Fraser (1997) states that a strategic combination of guessing and dictionary use was the most effective way to deal with L2 reading comprehension. Results also revealed that consulting a dictionary was associated with substantial vocabulary learning.
Songhao (1997) also remarks the positive effects of the dictionary use and how learners seem to have the need to confirm their guess and clarify their confusions with the dictionary.
Cote and Tejedor (1998) reveal the "widespread ignorance" about dictionary use on the students’ part. Most students thought they were good at using a dictionary. It was observed that the students did not pay attention to the dictionary entry on the whole, but just looked for the L1 equivalent.
Atkins and Varentola (1998) Lower proficiency students tend to use dictionaries more often in reading comprehension process. Lower proficiency EFL students did better with dictionaries than without dictionaries. No difference was found among higher proficiency students.
Prichard (2008) The findings suggest that high-intermediate and advanced learners are often selective when considering whether to look up a word. However, a third of the participants in the study were judged to have used the dictionary excessively. A quarter of the words were not essential for reading comprehension of the author's main points, nor "frequent or useful words," according to corpus research. It is concluded that some learners might benefit from training in selective dictionary use.
Mármol and Sánchez-Lafuente (2013) revealed that dictionary use is not efficient as expected. Yet, a positive attitude towards this tool prevails among the best performers.