\documentclass{article}
\usepackage{bidi}
\title{Testing \LaTeX's Default Tabular in \textsf{RTL} and \textsf{LTR}}
\author{Vafa Khalighi\thanks{Maintained by bidi-tex \url{https://github.com/bidi-tex}}}
\newcommand{\rb}[1]{\raisebox{1.5ex}[0mm]{#1}}
\begin{document}
\maketitle
In this document we test \LaTeX's default tabular in \textsf{RTL} and \textsf{LTR}.
\section{LTR}
\begin{center}\small
\begin{tabular}{|l||c|l|c|l|c|l|}
\hline
& \multicolumn{2}{c|}{6.15--7.15 pm} & \multicolumn{2}{c|}{7.20--8.20 pm}
& \multicolumn{2}{c|}{8.30--9.30 pm} \\ \cline{2-7}
&& Teacher && Teacher && Teacher \\ \cline{3-3}\cline{5-5}\cline{7-7}
\rb{Day} & \rb{Subj.} & Room & \rb{Subj.} & Room & \rb{Subj.} & Room\\
   \hline\hline
&& Dr.~Smith && Ms.~Clark && Mr.~Mills\\
\cline{3-3}\cline{5-5}\cline{7-7}
\rb{Mon.} & \rb{UNIX} & Comp. Ctr & \rb{Fortran} & Hall A
  & \rb{Math.} & Hall A \\ \hline
&& Miss Baker && Ms.~Clark && Mr.~Mill\\
\cline{3-3}\cline{5-5}\cline{7-7}
\rb{Tues.} & \rb{\LaTeX} & Conf.~Room & \rb{Fortran} & Conf~Room
  & \rb{Math.} & Hall A \\ \hline
&& Dr.~Smith && Dr.~Jones && Dr.~Jones \\
\cline{3-3}\cline{5-5}\cline{7-7}
\rb{Wed.} & \rb{UNIX} & Comp. Ctr & \rb{C} & Hall A
  & \rb{ComSci.} & Hall A \\ \hline
&& Miss Baker && Ms. Clark & \multicolumn{2}{c|}{} \\
\cline{3-3}\cline{5-5}
\rb{Fri.} & \rb{\LaTeX} & Conf.~Room & \rb{C++} & Conf.~Room
& \multicolumn{2}{c|}{\rb{canceled}}\\ \hline
\end{tabular}\end{center}
\section{RTL}

\setRTL
\begin{center}\small
\begin{tabular}{|r||c|r|c|r|c|r|}
\hline
& \multicolumn{2}{c|}{6.15--7.15 pm} & \multicolumn{2}{c|}{7.20--8.20 pm}
& \multicolumn{2}{c|}{8.30--9.30 pm} \\ \cline{2-7}
&& Teacher && Teacher && Teacher \\ \cline{3-3}\cline{5-5}\cline{7-7}
\rb{Day} & \rb{Subj.} & Room & \rb{Subj.} & Room & \rb{Subj.} & Room\\
   \hline\hline
&& Dr.~Smith && Ms.~Clark && Mr.~Mills\\
\cline{3-3}\cline{5-5}\cline{7-7}
\rb{Mon.} & \rb{UNIX} & Comp. Ctr & \rb{Fortran} & Hall A
  & \rb{Math.} & Hall A \\ \hline
&& Miss Baker && Ms.~Clark && Mr.~Mill\\
\cline{3-3}\cline{5-5}\cline{7-7}
\rb{Tues.} & \rb{\LaTeX} & Conf.~Room & \rb{Fortran} & Conf~Room
  & \rb{Math.} & Hall A \\ \hline
&& Dr.~Smith && Dr.~Jones && Dr.~Jones \\
\cline{3-3}\cline{5-5}\cline{7-7}
\rb{Wed.} & \rb{UNIX} & Comp. Ctr & \rb{C} & Hall A
  & \rb{ComSci.} & Hall A \\ \hline
&& Miss Baker && Ms. Clark & \multicolumn{2}{c|}{} \\
\cline{3-3}\cline{5-5}
\rb{Fri.} & \rb{\LaTeX} & Conf.~Room & \rb{C++} & Conf.~Room
& \multicolumn{2}{c|}{\rb{canceled}}\\ \hline
\end{tabular}\end{center}
\end{document}
