five_number_summary <- iris %>% 
  group_by(Species) %>% 
  summarise_at(vars(Sepal.Length),
               list(min=min, Q1=~quantile(., probs = 0.25),
                    median=median, Q3=~quantile(., probs = 0.75),
                    max=max))
five_number_summary
# A tibble: 3 x 6
  Species      min    Q1 median    Q3   max
  <fct>      <dbl> <dbl>  <dbl> <dbl> <dbl>
1 setosa       4.3  4.8     5     5.2   5.8
2 versicolor   4.9  5.6     5.9   6.3   7  
3 virginica    4.9  6.22    6.5   6.9   7.9